(1) Field of the Invention
The present invention relates generally to anti-skid control system and method for an automotive vehicle which can prevent each of road wheels from being locked by performing cyclical pressure increase and decrease controls of a brake liquid pressure during the braking of a wheel cylinder equipped on each of the road wheels of the automotive vehicle and, more particularly, techniques adopted in the anti-skid control system and method such as a small sizing of a liquid pressure pump equipped in the anti-skid control system for a circulation of a working liquid and a suppression of vibration due to an excessive drive of the liquid pressure pump.
(2) Description of the Related Art
A Japanese Patent Application First Publication No. Heisei 7-117653 published on May 9, 1995 exemplifies a previously proposed brake liquid pressure controlling apparatus.
In the previously proposed brake liquid pressure controlling apparatus, in accordance with a correlation between a pseudo vehicle body velocity and each road wheel velocity, namely, in accordance with a road wheel slip rate of each road wheel, a pressure increase or decrease control for the road wheel corresponding wheel cylinder is carried out so that such a slip rate suppression control that each or any one of the road wheels does not exceed a predetermined value (so-called, a control target velocity) is carried out to prevent the occurrence of the corresponding road wheel""s lock.
Since a maximum road wheel velocity from among the respective wheel velocities of the road wheels is approximated to an actual vehicle body velocity, this maximum road wheel velocity is used for a control purpose as a pseudo vehicle body velocity. However, the maximum wheel velocity may probably be calculated at a value higher than an actual vehicle body velocity due to the slips of some road wheels, an unnecessary pressure reduction control of the brake liquid pressure is started so that a brake insufficient state of the vehicle may occur if the pseudo vehicle body velocity based on the maximum road wheel velocity is directly used. Hence, an offset value toward a lower vehicle velocity side is set to the vehicle body velocity based on the maximum road wheel velocity. It is common practice that the pseudo vehicle body velocity set toward a lower value by the velocity reduction side offset value than the pseudo vehicle body velocity based on the maximum road wheel velocity is used for an anti-skid control purpose.
However, since, in the previously proposed brake liquid pressure controlling apparatus described above, the pseudo vehicle body velocity which is set to the lower value by the offset quantity toward the lower velocity side than the pseudo vehicle body velocity based on the maximum road wheel velocity, the control target velocity (so-called, a threshold value determining a start of the pressure decrease control) of the road wheel velocities generated on the basis of the pseudo vehicle body velocity is also set to be the lower value. Thus, since the pressure increase control is acted upon even when the road wheel velocity becomes deeper (or lower) than an ideal road wheel velocity with respect to the actual vehicle body velocity, the pressure increase becomes excessive. Hence, during the subsequent pressure decrease control, the increase in the pressure increase quantity, i.e., a quantity (consumed liquid quantity) of the brake liquid circulated toward a master cylinder side from a reservoir along with a discharge of a relatively excessive quantity of brake liquid from the wheel cylinder to the reservoir. A liquid pressure pump having a larger capacity is required and a cost of installing the anti-skid control system becomes expensive and a large sizing of the whole system is brought out. In addition, due to a frequent operation of the liquid pressure pump, a performance of a sound suppression in the liquid pressure pump and a brake piping system can be worsened.
It is, therefore, an object of the present invention to provide anti-skid control system and method for an automotive vehicle which enable a whole reduction in a consumed liquid quantity of a working liquid.
According to one aspect of the present invention, there is provided an anti-skid control system for an automotive vehicle, comprising: a brake unit to adjust a brake liquid pressure of a wheel cylinder installed on each road wheel of the vehicle, the brake unit being enabled to form any one of a pressure increase state, a pressure decrease state, and a pressure hold state in each wheel cylinder; a wheel velocity detecting section that detects wheel velocities of the respective road wheels; a pseudo vehicle body velocity calculating section that calculates a pseudo vehicle body velocity on the basis of the detected road wheel velocities of the respective road wheels; a road wheel deceleration calculating section that calculates a deceleration of each of the road wheels; a vehicle body deceleration calculating section that calculates a pseudo vehicle body deceleration from the calculated pseudo vehicle body velocity; and a brake control unit that, when any one of the wheel velocities of the respective road wheels has reached to a target velocity derived on the basis of the pseudo vehicle body velocity, forms the pressure decrease state of the brake unit to execute such a pressure decrease control as to carry out a decrease in pressure of the brake liquid of any one of the wheel cylinders which corresponds to one of the road wheels whose detected wheel velocity has reached to the target velocity and, thereafter, when the calculated wheel deceleration of the corresponding one of the road wheels becomes equal to or below zero, forms the pressure increase state of the brake unit to execute such a pressure increase control as to carry out an increase in pressure of the brake liquid of the corresponding one of the wheel cylinders, the brake control unit suspending the pressure increase control and executing such a pressure hold control as to hold the brake liquid pressure of the road wheel corresponding one of the wheel cylinders when the calculated wheel deceleration of the corresponding one of the road wheels has reached to a predetermined deceleration set on the basis of the vehicle body deceleration.
This summary of the invention does not necessarily describe all necessary features so that the invention may also be a sub-combination of these described features.